1. Field of the Invention
The present invention relates to a duplex radio communication transceiver and, more particarly, to a structure of parts to be used in a transceiver for duplex radio communications such as a mobile telephone, which structure is intended to reduce the size of a high-frequency part including a duplexer for coupling an antenna, a transmitting part and a receiving part.
2. Description of the Prior Art
In order to facilitate the handling and portage of a transceiver for duplex radio communications such as a mobile transceiver, it is remarkably important to make the entire transceiver small-sized and handy.
The transceiver described above is composed essentially of an antenna for transmitting and receiving radio waves of multiple frequencies, a duplexer for coupling the antenna and the transmitting and receiving parts of the transceiver, a receiving high-frequency part for converting the received signal of the duplexer into a signal of lower frequency, and a transmitting high-frequency part for increasing the frequency of and controlling the power of a signal to be transmitted and for coupling it to the duplexer.
Prior art duplexers have a problem of a large volume because they use a filter in which several cavity resonators containing ceramics or the like having a high relative dielectric constant are incorporated in a tandem connection (for example, four or five for the transmitting filter elements and five or six for the receiving filter elements).
Since, moreover, the cavity resonators used in prior art duplexers have large volumes, a receiving low-noise amplifier and a receiving second filter composed of the cavity resonators like the above-mentioned (e.g., three cavity resonators in tandem connection) are fabricated as separate circuit elements, which are connected on the mother board of the transceiver.
This makes it difficult to reduce the size of the transceiver because of the large volumes of the individual circuit elements and the large dead spaces for their connections.
As a result, it is a serious concern for portable telephones or the like having an earnest demand for size reduction to reduce the size of the duplexers including the low-noise amplifier and the receiving second filter.
On the other hand, the transmitting high-frequency part is composed of a power amplifier for amplifying the low power (of 0.1 to 1 mW) of a high-frequency signal (of several tens MHz to several GHz) into a high power (of several W), and a driver amplifier for coupling the output of the power amplifier in an optimum state to the duplexer. Since the transceiver according to the prior art is manufactured such that those amplifiers are separately made into a module and arranged, the volumes occupied by the amplifiers are increased to raise a problem of making it difficult to reduce the size of the transceiver.
In order to solve this problem, it is conceivable to form the driver amplifier and the power amplifier on a common heat-sink substrate or metallic substrate to make a single module. In this case, however, it is substantially impossible to check up the matching condition of the inside of the module using five or six bipolar transistors or FETs. As a result, the transceiver of the prior art is accompanied by a defect that its control takes a very long time so that its mass-productivity is deteriorated.